8.1.2 Traditional GNU Objective-C runtime API

The GNU Objective-C runtime used to provide a different API, which we
call the “traditional” GNU Objective-C runtime API. Functions
belonging to this API are easy to recognize because they use a
different naming convention, such as class_get_super_class()
(traditional API) instead of class_getSuperclass() (modern
API). Software using this API includes the file
objc/objc-api.h where it is declared.

Starting with GCC 4.7.0, the traditional GNU runtime API is no longer
available.